In its simplest form, a gas turbine engine, of the type typically used in aviation applications, includes, in serial flow communication, a fan section, through which ambient air is drawn into the engine, a compressor for pressurizing the incoming air, a combustor, in which the high pressure air is mixed with atomized fuel and ignited, and a turbine section that extracts the energy from hot gas effluent to drive the compressor and fan, producing desired engine thrust. An augmentor is used primarily to provide extra thrust for relatively short periods of time, which may be required during e.g., takeoff and high speed maneuvers, and can also be included to increase the thrust generated by the engine.
To initiate combustion of the fuel and air mixture within the combustor, a conventional gas turbine engine includes an ignition system comprising an ignition exciter component, at least one igniter plug and an ignition lead assembly coupled between the exciter component and the igniter plugs. The ignition exciter converts ac or dc input power into high voltage high current electrical impulses that are periodically delivered to the igniter plugs to facilitate engine starting. The ignition lead assemblies are electrical conduits that transfer electrical energy between the ignition exciter and the igniter plugs(s). The igniter plugs convert electrical energy into thermal energy, such as an ignition spark, which initiates the combustion process.
In aviation large gas turbine applications, the ignition leads constitute a significant portion of the ignition system weight and cost. Specifically, each lead assembly includes an igniter cable comprising a stranded center conductor encased within electrical insulation and housed within a flexible conduit. The lead assembly conduits must be cooled to minimize degradation thereof resulting from exposure to the high operating temperatures within the engine. In some applications, the ignition leads are air cooled, utilizing fan or compressor bleed air to continuously cool the lead assemblies. The addition of active cooling greatly increases the ignition lead conduit diameter and necessitates the introduction of an integral “Y” shaped fitting on the ignition lead conduit to facilitate interconnection to the cooling air supply.
Ignition leads likewise represent a maintenance burden since they are often damaged during routine engine inspection and maintenance activities. Additionally, environmentally induced thermal and vibratory stresses degrade ignition lead component parts over time necessitating periodic repair and/or overhaul. Indeed, during operation, the center conductor of the ignition lead tends to chafe on the internal conduit and supporting splines. Likewise, the external conduit/braid features of the ignition lead chafe and are damaged by nearby components or structures. Further, the elastomeric seals and center conductor insulation of each of the leads can be thermally degraded by the extremely high temperatures and pressure variations within the operating environment.
Unlike aeroderivative turbine applications, or heavy frame industrial turbine applications, aviation turbine ignition system components are frequently mounted directly on the engine and must operate in extremely harsh environments. As such, ignition systems directed for use in aviation turbine applications require designs that are compact size and minimize the overall weight of the engine. Accordingly, elimination of the ignition leads from an ignition system for a gas turbine engine would be very desirable.
In addition to eliminating the associated cost, weight and maintenance issues, a leadless ignition system would offer improved efficiency over prior art large gas turbine ignition systems. In particular, a typical ignition lead contributes about 35% to the overall ignition system electrical losses.
As such, the invention provides an ignition system that can be directly mounted to the housing of a large gas turbine engine, the system includes an exciter component directly connected to an igniter, eliminating the requirement for an ignition lead connection therebetween. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.